Symmetricom SSU-2000 User Manual page 174

Chapter 7 Input Module Reference Data
1-Port and 3-Port DS1 Input Modules
Alarms Caused by Hardware Problems
The following alarms are generated due to hardware problems:
External Clock Signal PLL Unlocked
– Report event message and perform any other actions as required by the
user-set severity level
– Fault channel, even if severity is less than MAJOR
– Monitor PLL for recovery
Input Signal PLL Unlocked
– Report event message and perform other actions as required by severity
– Fault port, regardless of severity
– Monitor PLL for recovery
Phase Measurement Circuitry Fault
– Report event message and perform any other required actions
– Fault Port
– Monitor phase hardware for recovery
Handling Input Signal Faults
The following alarms are caused by problems with the incoming input signal's
formatting or content:
Errors Tracked:
– Framed signals: LOS, AIS, OOF, BPV and CRC
– Unframed signals: LOS
Error and Clear Counters
The Input module maintains a count of the number of consecutive errored seconds
for each error type for each port. Once this error count exceeds a user-set limit, the
input signal which has experienced the errors is said to be in episode.
The Input module maintains a count of the number of consecutive seconds in which
the input signal for each port was free of each type of error. This clear count must
exceed a user-set limit before the input signal is no longer in episode.
Handling Input Signal Faults
For LOS (loss of signal) and before going into episode:
Coast over brief occurrences of LOS, reporting the last known good phase
measurements for the port until signal returns or the signal goes into episode
The duration of a brief occurrence of LOS is defined by the value of the error
count for LOS
Once in episode:
Log LOS alarm, taking appropriate action per the assigned severity level
Invalidate current phase measurements
174 SSU-2000 User's Guide 12713020-002-2 Revision F.01 – January 2007